LINUS PAULING INSTITUTE SPRING/SUMMER 2005 RESEARCH REPORT
Preventing Osteoporosis through Diet and Lifestyle
Jane Higdon, Ph.D.
Osteoporosis is a condition that leads to fragile bones and increases the risk of a wrist, hip, or spine fracture. Screening tests, which are noninvasive and painless, measure bone mineral density (BMD) of the hip, spine, wrist, or heel. The diagnosis of osteoporosis is made when a person’s BMD is substantially less then the average BMD for young adults. A related condition called osteopenia, or low bone mass, is less severe but still indicates low BMD. It has been estimated that as many as 10 million Americans over the age of 50 have osteoporosis and another 34 million have osteopenia. Although commonly thought of as a problem for women, osteoporosis also affects men. Of the 10 million Americans with osteoporosis, about 2 million are men. A number of factors have been identified that contribute to an individual’s risk of developing osteoporosis (see box on page 9). Some of those risk factors cannot be changed, while others, such as those that involve diet and lifestyle, are modifiable.
Since bone is a dynamic living tissue that gets stronger when stressed and weaker when not used, physically active people generally have higher BMD at all ages than people who are sedentary. Weight-bearing exercise and strength training are most effective at increasing or maintaining bone mass. During weight-bearing exercise like walking, running, dancing, or stair climbing, muscular and gravitational forces stress bone. Strength training increases the amount of force that muscles exert on bones. In addition to improving or maintaining BMD, strength training has been found to prevent falls—the most common cause of hip and wrist fractures—in people even in their 90s. Activities that improve coordination and balance, such as Tai Chi, may also help prevent falls. Although swimming and cycling are excellent activities for improving cardiovascular fitness, balance, and coordination, they are less effective for maintaining BMD because they are not weight-bearing. If you already have osteoporosis, consult a knowledgeable healthcare provider before starting an exercise program.
Inadequate calcium intake during childhood and adolescence can impair bone development and may prevent the attainment of optimal peak bone mass during early adulthood. In older adults inadequate calcium intake accelerates bone loss and likely contributes to the development of osteoporosis. Although the importance of calcium to bone health is well-recognized, adequate calcium intake alone is not enough to prevent bone loss that could lead to osteoporosis and osteoporotic fracture. An 8-ounce serving of calcium-fortified orange juice or nonfat milk or yogurt provides about 300 mg of calcium. Most calcium supplements, including calcium carbonate, are best absorbed when taken with food, but calcium citrate and calcium citrate malate are also well-absorbed on an empty stomach.
Although it has long been known that severe vitamin D deficiency adversely affects bone health, recent research suggests that marginal vitamin D deficiency is common and increases the risk of osteoporosis. When vitamin D is metabolized to its most active form, it increases the intestinal absorption of calcium and prevents urinary calcium loss. Without sufficient vitamin D, calcium absorption is not efficient enough to satisfy the body’s needs, even when calcium intake is adequate. Vitamin D is synthesized in the skin when exposed to ultraviolet-B (UVB) radiation from sunlight and can be obtained from the diet. Very little UVB radiation reaches the earth above 37 degrees of latitude from November through February, so people who live north of 37 degrees produce little if any vitamin D during late fall and winter (see map). The application of sunscreen with an SPF factor of 8 reduces skin production of vitamin D by 95% even in summer. The ability to synthesize vitamin D in the skin also decreases with age. A 70-year-old makes only 25% of the vitamin D made by a 20-year-old exposed to the same amount of sunlight. Few foods other than fatty fish are naturally rich in vitamin D. In the U.S., milk has been fortified with vitamin D (400 IU/quart) since the 1940s, which has virtually eliminated rickets. Some brands of breakfast cereal and orange juice are also fortified with vitamin D.
Fruits and vegetables
Fruits and vegetables are rich in several nutrients that appear to play important roles in bone health, including potassium, magnesium, and vitamin K. Several epidemiological studies have found that higher intakes of fruits and vegetables, particularly those rich in potassium, are associated with higher BMD and lower risk of fracture in older adults. Fruits and vegetables are rich in precursors to bicarbonate ions, which can preserve calcium in bones by buffering organic acids consumed in the diet or generated metabolically. The Dietary Approaches to Stop Hypertension (DASH) studies have also reported that high fruit and vegetable intake may improve bone health. Originally designed to test the effect of diet on blood pressure, the DASH trial compared three diets: a control diet that provided only 3 servings of fruits or vegetables, a diet that provided about 8 servings of fruits or vegetables, and a diet that provided 8 servings of fruits or vegetables and 3 servings of low-fat dairy products (now called the DASH diet). In addition to lowering blood pressure, both fruit- and vegetable-rich diets reduced urinary calcium loss, and the DASH diet lowered biochemical markers of bone turnover, particularly bone resorption (loss). Taken together, the results of epidemiological and clinical trials suggest that a diet rich in fruits and vegetables that contains adequate calcium and vitamin D may help prevent bone loss.
The role of dietary protein in bone health is complex. While high protein intakes have been found to increase urinary calcium excretion in small, short-term studies, several large population-based studies have found that low protein intakes are associated with more rapid BMD loss and increased fracture risk in older adults.
Higher salt intakes appear to increase urinary calcium loss, although this effect can be modified by other dietary factors. The DASH-sodium trial compared the DASH diet with a typical western diet at three levels of salt intake. Urinary calcium loss increased with dietary salt intake on both diets, but urinary calcium losses were greater at every level of salt intake in those on the typical western diet.
Excess vitamin A (retinol)
The results of several epidemiological studies suggest that the long-term intake of more than 5,000 IU/day of preformed vitamin A (retinol) is associated with decreased BMD and increased risk of osteoporotic fracture in older men and women. Only high intakes of retinol—not beta-carotene—were associated with adverse effects on bone health. Although 5,000 IU is considerably higher than the RDA for vitamin A (3,000 IU for men and 2,333 IU for women), it is not uncommon for multivitamin supplements to contain 5,000 IU of retinol.
When lifestyle changes aren’t enough
In some cases, lifestyle modification is not enough to prevent osteoporosis or, more importantly, osteoporotic fractures. Fortunately, several medications are now available for the effective treatment of osteoporosis. The National Osteoporosis Foundation Web site (nof.org) is an excellent resource for information about osteoporosis prevention and treatment as well as tips for finding a physician who is knowledgeable about the treatment of osteoporosis.
Last updated May, 2005
Micronutrient Research for Optimum Health
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